markdown: Add indented versions of multi-line Markdown macros.

This is part of our efforts to change our integrations/webhooks
docs to follow the same sort of numbered-list format as our /help
docs. In order to indicate that paragraphs separated by newlines
are part of the same numbered-list point, every paragraph must be
indented 4 spaces.

tools/linter_lib/custom_check.py

@@ -699,6 +699,8 @@ def build_custom_checkers(by_lang):
             "templates/zerver/integrations/perforce.md",
             # Has some example code that could perhaps be wrapped
             "templates/zerver/api/webhook-walkthrough.md",
+            # This macro has a long indented URL
+            "templates/zerver/help/include/git-webhook-url-with-branches-indented.md",
         }
         for fn in by_lang['md']:
             max_length = None